Pilots for Ireland-based Ryanair have announced that they will strike beginning on Dec. 20, just days before Christmas, one of the busiest travel seasons of the year, and could impact thousands of flights.

A majority of the 84 Ryanair pilots voted as part of the Irish Air Pilots’ Association trade union to back a strike over the weekend in a secret ballot, The Independent reported. Strikes will also take place in Italy and Germany at different times.

The Italian contingent plans a four-hour strike on Dec.15, while the German pilots said they would avoid the Christmas holidays from Dec. 23-26 when it strikes, The Independent reported. Pilots want better working conditions, and most have refused the pay increases offered by the airline.

“Ryanair will deal with any such disruptions if, or when they arise, and we apologize sincerely to customers for any upset or worry this threatened action by less than 28 percent of our Dublin pilots may cause them over the coming days,” the airline said in a statement, The Independent reported. “While some disruption may occur, Ryanair believes this will be largely confined to a small group of pilots who are working their notice and will shortly leave Ryanair, so they don’t care how much upset they cause colleagues or customers.”

The airline does not recognize unions, and the 79 pilots who voted to strike are only a small part of the more than 360 Ryanair pilots who fly out of Dublin, the BBC reported. Ryanair has cancelled about 20,000 flights since September, which has affected pilots’ pay and schedules.